Hi Everyone,
This is my first post ever and I've been doing some good research but I haven't found anyone in my predicament yet. I have a room where whatever projector I make will be sitting about 12 feet away from the wall and I need to limit my screen size to approx 11-12 feet in diagonal.
The image above presents what the OHP projects. The big rectangular shadow in the middle is what a Lilliput 7'' screen would look like on the wall. If my BenQ is 15'' in diagonal, my image is going to be projecting on the ceiling and the floor at the same time if it sits on top of my OHP.
So- needless to say, big problems and I haven't found a post regarding the distance between the PJ and the wall with regards to controlling the image from getting too big.
What would you all do if you were presented with the same situation?
I have the following already for my project:
3M 9550 OHP
BenQ FP531 (1024x768) coming in the mail and I can't wait to strip it!
Approach #1 for big screen project:
Strip BenQ and do traditional overlay on top of OHP.
Approach #2 for big screen project:
Remove OHP overhead arm and turn it on it's side to mount it into a PJ box. Strip BenQ and slide LCD panel into PJ box so I can adjust it to fit whatever size image I need on the wall. Remove 3 piece lens from overhead arm and mount it into the center of the front panel of the PJ box to project the image onto the wall.
Approach #3 for big screen project:
Strip both BenQ and OHP and put parts all willy nilly into PJ box so it resembles approach 2 but w/o the casing of the OHP at the rear of the PJ box.
Approach #4 for big screen project:
Sell 3M 9550 and just go with the more traditional route of tinkering around with fresnels/power sources/bulbs/lens and fitting it all into the PJ box like the rest of you have done.
Approach #5 for big screen project:
What would all of you do in my situation?
I can see that approach 4 has been done A TON of times however there are some areas I don't trust myself to really perform.
Area of concern #1: Locating the proper power supply.
Area of concern #2: Finally settling on the best overall light bulb to use and creating the reflecting areas in the bulb section of the PJ so the light reflects evenly onto the fresnel.
Area of concern #3: Cutting the fresnel in half. I JUST realized that you guys/gals have been cutting the fresnel in half to take advantage of what each side can do. I actually still don't understand how you all have calculated the proper distance between the fresnel/lcd/2nd fresnel.
Please help.
Thank you all!
Clifford
This is my first post ever and I've been doing some good research but I haven't found anyone in my predicament yet. I have a room where whatever projector I make will be sitting about 12 feet away from the wall and I need to limit my screen size to approx 11-12 feet in diagonal.
An externally hosted image should be here but it was not working when we last tested it.
The image above presents what the OHP projects. The big rectangular shadow in the middle is what a Lilliput 7'' screen would look like on the wall. If my BenQ is 15'' in diagonal, my image is going to be projecting on the ceiling and the floor at the same time if it sits on top of my OHP.
So- needless to say, big problems and I haven't found a post regarding the distance between the PJ and the wall with regards to controlling the image from getting too big.
What would you all do if you were presented with the same situation?
I have the following already for my project:
3M 9550 OHP
BenQ FP531 (1024x768) coming in the mail and I can't wait to strip it!
Approach #1 for big screen project:
Strip BenQ and do traditional overlay on top of OHP.
Approach #2 for big screen project:
Remove OHP overhead arm and turn it on it's side to mount it into a PJ box. Strip BenQ and slide LCD panel into PJ box so I can adjust it to fit whatever size image I need on the wall. Remove 3 piece lens from overhead arm and mount it into the center of the front panel of the PJ box to project the image onto the wall.
Approach #3 for big screen project:
Strip both BenQ and OHP and put parts all willy nilly into PJ box so it resembles approach 2 but w/o the casing of the OHP at the rear of the PJ box.
Approach #4 for big screen project:
Sell 3M 9550 and just go with the more traditional route of tinkering around with fresnels/power sources/bulbs/lens and fitting it all into the PJ box like the rest of you have done.
Approach #5 for big screen project:
What would all of you do in my situation?
I can see that approach 4 has been done A TON of times however there are some areas I don't trust myself to really perform.
Area of concern #1: Locating the proper power supply.
Area of concern #2: Finally settling on the best overall light bulb to use and creating the reflecting areas in the bulb section of the PJ so the light reflects evenly onto the fresnel.
Area of concern #3: Cutting the fresnel in half. I JUST realized that you guys/gals have been cutting the fresnel in half to take advantage of what each side can do. I actually still don't understand how you all have calculated the proper distance between the fresnel/lcd/2nd fresnel.
Please help.
Thank you all!
Clifford
picture too big for room!
Well, you've figured out the most common problem with large LCD panels! If you want to make a reasonable-sized image without your projector sitting in the middle of the picture, then you will need a long-throw lens. I have a media room where I need an image <95 inches from a throw distance of 14 feet, since I want to put the projector on a counter at the back of the room. To get that with a 15" monitor panel, I need a lens with a focal length of about 571 mm. Pretty far from the 320 mm fl of most OHPs.
Triplets are outstanding for use at lower focal lengths, since they can accept a 45 degree angle field. That corresponds to the angle you need for making a large image from a near distance. I have never seen a triplet lens with a focal length longer than 500 mm on any auction, webstore, etc. I suspect nobody makes them because you don't need anything that fancy to make a workable lens with >500 mm fl. I have four different lenses to try with my projector:
1. Single meniscus lens 72 mm diameter, 571 mm fl: based on a Rolyn acrylic positive meniscus lens for <$9 US. This is optically identical to a 1.75 Diopter reading glasses lens, but with a large round shape.
2. Symmetric duplet lens 70 mm diameter, 526 mm fl: Based on two Rolyn acrylic positive meniscus lenses for <$9 each.
3. 700 mm fl achromatic telescope objective I got from an eBay auction for $10.
4. 100 mm diameter 580 mm fl acromatic lens I made from two simple lenses I got from surplusshed.com for $8.
From simple preliminary tests, I think #2 is working the best.
Now for your other concerns:
Area of concern #1: Locating the proper power supply.
For the LCD panel? It is probably just a DC wallwart box. See if the power socket on the monitor says something like "12 VDC 1A" and shows a little polarity drawing. Then go to Radio Shack or someplace like that and show it to them.
Area of concern #2: Finally settling on the best overall light bulb to use and creating the reflecting areas in the bulb section of the PJ so the light reflects evenly onto the fresnel.
There is really no question: You need a Metal Halide bulb of around 250-400 Watts, with a color temperature of at least 4200 K. (5000-6000 is better) Small ones are easier to fit with condensors and reflectors. You can use a simple soup ladle or spherical mixing bowl as a reflector. Depends on the size of your bulb.
Area of concern #3: Cutting the fresnel in half. I JUST realized that you guys/gals have been cutting the fresnel in half to take advantage of what each side can do. I actually still don't understand how you all have calculated the proper distance between the fresnel/lcd/2nd fresnel.
OHP fresnels tend to be two lenses glued together around the edges. Some are not glued. If you use them both below the LCD, then there is no reason to cut them apart. Either way, the fresnels have to be at least 1" from the LCD or their rings will show up in the projected image. The reason to put the upper fresnel above or below the LCD, or to move them around a bit, is to get the light focussed into the projector lens. This tends to be an iterative process: Focus the image, then focus the condensor system, repeat...
This can be calculated (see free excell download at diybuildergroup.com), but even so people still end up fiddling around a bit to get it right.
If I were you, I would sell the OHP and build a box. The only part you could use from the OHP is the lower fresnel. Seems silly to trash the whole OHP just for that.
Well, you've figured out the most common problem with large LCD panels! If you want to make a reasonable-sized image without your projector sitting in the middle of the picture, then you will need a long-throw lens. I have a media room where I need an image <95 inches from a throw distance of 14 feet, since I want to put the projector on a counter at the back of the room. To get that with a 15" monitor panel, I need a lens with a focal length of about 571 mm. Pretty far from the 320 mm fl of most OHPs.
Triplets are outstanding for use at lower focal lengths, since they can accept a 45 degree angle field. That corresponds to the angle you need for making a large image from a near distance. I have never seen a triplet lens with a focal length longer than 500 mm on any auction, webstore, etc. I suspect nobody makes them because you don't need anything that fancy to make a workable lens with >500 mm fl. I have four different lenses to try with my projector:
1. Single meniscus lens 72 mm diameter, 571 mm fl: based on a Rolyn acrylic positive meniscus lens for <$9 US. This is optically identical to a 1.75 Diopter reading glasses lens, but with a large round shape.
2. Symmetric duplet lens 70 mm diameter, 526 mm fl: Based on two Rolyn acrylic positive meniscus lenses for <$9 each.
3. 700 mm fl achromatic telescope objective I got from an eBay auction for $10.
4. 100 mm diameter 580 mm fl acromatic lens I made from two simple lenses I got from surplusshed.com for $8.
From simple preliminary tests, I think #2 is working the best.
Now for your other concerns:
Area of concern #1: Locating the proper power supply.
For the LCD panel? It is probably just a DC wallwart box. See if the power socket on the monitor says something like "12 VDC 1A" and shows a little polarity drawing. Then go to Radio Shack or someplace like that and show it to them.
Area of concern #2: Finally settling on the best overall light bulb to use and creating the reflecting areas in the bulb section of the PJ so the light reflects evenly onto the fresnel.
There is really no question: You need a Metal Halide bulb of around 250-400 Watts, with a color temperature of at least 4200 K. (5000-6000 is better) Small ones are easier to fit with condensors and reflectors. You can use a simple soup ladle or spherical mixing bowl as a reflector. Depends on the size of your bulb.
Area of concern #3: Cutting the fresnel in half. I JUST realized that you guys/gals have been cutting the fresnel in half to take advantage of what each side can do. I actually still don't understand how you all have calculated the proper distance between the fresnel/lcd/2nd fresnel.
OHP fresnels tend to be two lenses glued together around the edges. Some are not glued. If you use them both below the LCD, then there is no reason to cut them apart. Either way, the fresnels have to be at least 1" from the LCD or their rings will show up in the projected image. The reason to put the upper fresnel above or below the LCD, or to move them around a bit, is to get the light focussed into the projector lens. This tends to be an iterative process: Focus the image, then focus the condensor system, repeat...
This can be calculated (see free excell download at diybuildergroup.com), but even so people still end up fiddling around a bit to get it right.
If I were you, I would sell the OHP and build a box. The only part you could use from the OHP is the lower fresnel. Seems silly to trash the whole OHP just for that.
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